An electroplating process may be used in manufacturing semiconductor devices. Metal interconnect structures are formed on a silicon substrate, such as a silicon wafer, to provide electrical connections between transistors. Trenches are formed in the silicon substrate for depositing metal used to form the interconnect structures. Typically, a barrier layer and a seed layer of metal is then deposited on the silicon substrate. The silicon substrate is then immersed into an electroplating process chamber containing an electrolyte solution. Typically, an anode is then positioned in the electrolyte solution and a cathode is coupled to the silicon substrate for providing an electrical current. The electric current, electrolyte solution, and substrate then react to form a metal layer on the substrate surface, including in the trenches of the silicon substrate. Conductive process chamber contacts or fingers are typically used to position the silicon substrate in the electrolyte solution. These contacts may also be used to provide a current path.
A number of different types of contacts have been used in various electroplating process chambers. For example, U.S. Pat. No. 5,472,592 ("'592 Patent") entitled "Electrolytic Plating Apparatus and Method", inventor Kenneth J. Lowery, issued Dec. 5, 1995, which is incorporated by reference, describes an apparatus used in electroplating substrates. The '592 Patent describes an apparatus for plating a substrate positioned vertically. Three spring-like contacts are used to position a silicon wafer during the plating process. The '592 patent teaches a complex multichannel power supply and monitoring system, coupled to each contact which enables uniform plating.
U.S. Pat. No. 5,429,733 ("'733 Patent") entitled "Plating Device for Wafer", inventor Hirofumi Ishida, issued Jul. 4, 1995, which is incorporated by reference, also describes a plating device. The '733 Patent describes an apparatus for plating a silicon wafer positioned horizontally. Cathode electrodes and elastic members are used to position the silicon wafer against an air bag.
An EQUINOX single substrate processing system by SEMITOOL.RTM. also provides an electroplating process chamber having four to six contacts or "fingertips" for positioning a silicon wafer during the electroplating process.
After a metal layer is formed during the electroplating process, typically, the silicon substrate is removed from the electrolyte solution. The silicon substrate may be transferred to another process chamber, such as a spin/rinse/dry chamber. The electroplating process chamber contacts which may be covered with a residue of electrolyte solution then may become oxidized as they are exposed to oxygen. The contacts may even become oxidized if immersed into the electrolyte solution without the silicon substrate.
The oxidation of the contacts may cause undesirable consequences in subsequent electroplating. The oxidation of the contacts increases the resistance of the contacts. The increased resistance may also not be the same for each contact because some contacts may be more oxidized than others. Thus, a predetermined amount of voltage applied to each contact will create different amounts of current at the respective contacts. This increase and varying resistance of the contacts will cause nonuniform plating. Further, this oxidation of the contacts may even cause seed layer deplating at the portion of the silicon substrate which touches the contact.
The oxidized contacts may be cleaned with a solution such as, nitric acid. However, this cleaning process requires the electroplating process chamber to be taken off line and limits valuable manufacturing capability. Further, the contacts may have to be removed from the electroplating process chamber or replaced requiring further costly and complex maintenance tasks.
The '592 patent teaches a complex monitoring and multichannel power supply to enable uniform plating. However, the added complexity and components described in the '592 patent increases the cost and maintenance of the electroplating process chamber.
Therefore, it is desirable to provide a method for providing uniform electroplating on the surface of a silicon substrate without the increased costs associated with cleaning or replacing contacts. Further, it is desirable to have a method which does not require complex electronics or further components in an electroplating process chamber which increase the cost of maintaining and/or purchasing the electroplating process chamber.